High tidal claims

PREVIOUS claims that new power installations, particularly wind, would fuel this or that number of homes have frequently been overblown by as much as 20 times so how does the Pentland Firth tidal projection (your report, 20 January) stack up?

The two important factors are power (or energy production rate), measured in watts, and total energy produced, measured in watt-hours.

We know that about 18 kilowatt hour (kWh) per person per day is the average electrical energy used so for half the people of Scotland this would come to 2.5 x 18 gigawatt hour (gWh) per day. The projected maximum for Pentland is 1.9 x 24 gWh per day so, yes, a close match. But currently half of Scotland’s electricity production capacity is about 6 x 24 gWh per day, or three times as much. Why the discrepancy? The answer is that we do not use ­electricity at an average rate.

I do not have figures but let’s say that peak winter usage rate is at least three times average, then of course we will require a three times greater power source, so the Pentland Firth scheme could possibly fulfil the electricity needs of only one-sixth of the population.

Also we have to remember that electricity is only about one quarter of our internal energy requirements so we are back to that 20-fold exaggeration. Plus ça change!

(Dr) A McCormick

Kirkland Road

Terregles

Dumfries